Standard methods of cutting tissue may include using a scalpel, scissors, and radio frequency energy. Electrosurgical procedures and techniques using radio frequency energy are currently used since they generally reduce patient bleeding and trauma associated with cutting operations. Additionally, electrosurgical ablation procedures, where tissue surfaces and volume may be reshaped, cannot be duplicated through other treatment modalities.
Minimally invasive procedures in nerve and/or soft tissue such as the spine or the breast, however, are difficult to perform using standard scissors and scalpel. Furthermore, in a closed environment, radio frequency current dissipates into the surrounding tissue causing a decreased ability to achieve a current at the cutting electrode of sufficiently high density to initiate a cut. To overcome this problem, high power settings are often required to initiate the cut which often is painful and increases thermal damage to the tissue whether using a standard or a custom electrosurgical generator.
Another problem associated with cutting tissue is the control of bleeding. Radio frequency energy controls bleeding by coagulating small blood vessels. Another method of controlling bleeding is through the use of heat. For example, some commercially available scalpels use direct heat to control bleeding. However, while the bleeding is generally controlled, the cutting of tissue is often slower than with radio frequency energy and the knife edge readily dulls. Other commercially available scalpels use ultrasonic energy generally at 50 kHz to heat the tissue so as to coagulate severed blood vessels but cut slower than a standard electrosurgical electrode and are costly as a custom ultrasonic generator is required.
A further disadvantage of using radio frequency energy is the generation of smoke. The smoke is malodorous and can contain airborne viral particles that may be infectious. Furthermore, the smoke often obscures visualization of the procedure. When the smoke becomes too dense, the procedure is delayed until the smoke is released through one of the trocar ports and after enough carbon dioxide gas has reinsufflated the abdominal cavity. This unnecessarily prolongs the operative time.
Radiofrequency (RF) energy is used in a wide range of surgical procedures because it provides efficient tissue resection and coagulation and relatively easy access to the target tissues through a portal or cannula. Conventional monopolar high frequency electrosurgical devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a “cutting effect” along the pathway of localized tissue heating. Thus, the tissue is parted along the pathway of evaporated cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site. This collateral tissue damage often causes indiscriminate destruction of tissue, resulting in the loss of the proper function of the tissue. In addition, the device does not remove any tissue directly, but rather depends on destroying a zone of tissue and allowing the body to eventually remove the destroyed tissue.
Present electrosurgical techniques used for tissue ablation may suffer from an inability to provide the ability for fine dissection of soft tissue. The distal ends of electrosurgical devices are wide and flat, creating a relatively wide area of volumetric tissue removal and making fine dissections along tissue planes difficult to achieve because of the lack of precision provided by the current tip geometries.
In addition, identification of the plane is more difficult because the large ablated area and overall size of the device tip obscures the physician's view of the surgical field. The inability to provide for fine dissection of soft tissue is a significant disadvantage in using electrosurgical techniques for tissue ablation, particularly in arthroscopic, otolaryngological, and spinal procedures.
Traditional monopolar RF systems can provide fine dissection capabilities of soft tissue, but may also cause a high level of collateral thermal damage. Further, these devices may suffer from an inability to control the depth of necrosis in the tissue being treated. The high heat intensity generated by these systems causes burning and charring of the surrounding tissue, leading to increased pain and slower recovery of the remaining tissue. Further, the desire for an electrosurgical device to provide for fine dissection of soft tissue may compromise the ability to provide consistent ablative cutting without significant collateral damage while allowing for concomitant hemostasis and good coagulation of the remaining tissue.
Another problem with currently available RF nerve ablation devices is that they attempt to destroy nerve tissue from a central location including the tip of the device and a 3-D spherical or cylindrical zone around it. As a result, the further away the resecting ability is from the central zone the less effective the nerve destruction. Consequently, often the nerve is not adequately ablated leading to continued pain symptoms.
Further, the health care practitioner may have difficulty positioning the tip of the device in the optimal location to get an optimal and consistent clinical result. This may also result in unwanted necrosis of adjacent tissue, which can lead to clinical adverse events including subsequent repair of the necrotic tissue.
Other devices such as mechanical rongures can be used to remove soft tissue. However, these devices require the insertion of relatively large cannulas that further complicate the surgical procedure and can cause nerve compression and pain with variable clinical efficacy.
Accordingly, there is a need for devices and methods to provide efficient severing or cutting of nerve and/or soft tissue that can be used during a minimally invasive procedure and/or during an open surgical procedure. Further, there is also a need for devices and methods that provide fine dissection capabilities of nerve and/or soft tissue. Devices and methods that do not cause a high level of collateral thermal damage and allow for the control of necrosis in the tissue being treated are also needed. Devices and methods that provide efficient, controlled and safe debulking of tissue would also be beneficial.